For loops#

Loops are a way of telling the computer that we would like to perform an operation more than once. Let's take a look at how we write a loop in ImageJ Macro. It might seem complicated at first, but it's actually simple and powerful, and will be essential for ImageJ Macro programming. So much of automated image analysis is telling the computer "Repeat this tedious task 500 times so that I don't have to"

Let's dive in!

for (i=0; i<10; i++){ // (1)!
    print(i);
}

1. Remember what the ++ operator does from the variables section?

The first line defines the loop and its parameters. First we have the keyword for which tells the computer we'd like to execute a specific type of loop called a "for loop".

Next, we have three arguments that tell the for loop what we would like to to. These are i=0, i<10, and i++, separated by semicolons ;.

In this case, i is just a variable, like the ones we have seen before. It doesn't have to be i, you could call it anything you want, but i (for increment) is traditional in a for loop.

When this code is run, the first parameter i=0 will set the initial value of i to 0. Then, we will check the second parameter i<10 and ask "is i less than 10?". Because this is true, we will go on and execute whatever lines of code line within the curly braces {} (in this case, print the value of i). Then, the third parameter i++ will increment the value of i by 1.

We will then return to the top of the loop, except with the value of i set to 1 and repeat the exact same process. This will continue until we get to a condition where i is equal to 10. In this case, the check of the second parameter of the loop i<10 will fail, and the loop will exit.

Try changing some of the values in the loop and see what happens.